Simrad Robertson RF300 Testing

[R_C]

Originally Posted by tayana55

Can you send a photo or attach to this thread ?

Here are two photos. The red circles highlight the two green caps in question.

[tayana55]

Originally Posted by R_C

Here are two photos. The red circles highlight the two green caps in question.

Thanks for the photos.
I'm pretty certain that they are inductors

[R_C]

Thanks for the inductor tip. I'll do some investigating.

[mdejong]

Dear R C,

I have a Simrad AC12N autopilot together with parts that I "canabalized" from my broken Simrad AP14 autopilot. Unfortunately I do not have access to my rudder making it nearly impossible to install an RF300 rudder feedback unit. It is however very easy for me to design a circuit that determines the rudderposition based on counting the number of rotations of an axis inside the drive unit. I would however now need to emulate a RF300 unit.

When I was reading through this thread I noticed that you wrote that the RF300 produces a 3400 Hz signal at its center position with a 20 Hz change for every degree, so for -50 deg to + 50 deg the RF300 produces a 2400 to 4400 Hz signal. Is this correct? Do you know if I can use a square wave form or do I need to use a sinus? Do you also know the amplitude of the feedback signal?

Thanks in advance for any help/advise given,

[R_C]

mdejong,

That is correct. According to the RF300's specs it produces a 3400 Hz signal at center and +/- 20 Hz for each degree of change.

Unfortunately, I do not have a scope so I cannot test the RF300 directly. However, according to the help I received at Simulate an auto pilot's rudder feedback unit | Electro Tech Online the output of the 555 timer circuit I used to test is a square wave with an amplitude of a little under 12V.

[mdejong]

Dear R C, thanks for the information. I'll build some kind of emulating circuit (most likely by using a microprocessor). Out of curiosity, how did you power your 555 circuit? Did you power it by means of an external PSU or did you power it over the 2 connections wires?

I am wondering how Simrad manages to send a feedback signal to the auto pilot whilst powering the RF300 over the same wires. They must be superimposing the feedback signal onto a DC supply voltage but without a scope and a working RF300 it will be hard to find it out for myself.

[R_C]

mdejong,

I powered my circuit with the two connection wires. I tested voltage between the two RF300 connectors and ground on the J300 board. The one that tests close to the supply voltage I connected to Vcc on the 555 circuit. The other tests at about 1.1 VDC, which I connected to the 555's output pin. Oddly, it works without connecting the 555 circuit's ground to the J300 ground.

I want to learn more so I ordered a DSO yesterday. This will be my first use of an oscilloscope but I'll let you know what I learn when I look at the RF300's signal.

[mdejong]

RC, I agree that is seems odd not to connect the 555's GND. But if your simulator is working with a 2 wire connection, I will skip my idea of using a micoprocessor and simply use the 555 circuit design. I would be verycurious to see the wave form on an osiliscoop. Thanks again for the information, it is really usefull.

[SimradUser]

Hello, Did you ever get to testing an RF300 without hooking it to the simrad computer. I want to know how to test one without separately as in what equipment do I need to power it up and read the frequency from it.

Thanks.